1. Field of the Invention
For common aircraft carrying cargo, the cargo is usually palletized onto standardized flat pallets and standardized containers bases.
The present invention relates generally to systems to restrain cargo within airplanes and more specifically to cargo holddown devices used to lock standard cargo and container pallets in place within the aircraft. With greater particularity, this invention relates to pallet hold down systems which accommodate defective or distorted cargo pallet or cargo containers. Cargo pallets and cargo containers used in the aircraft industry must conform to government issued standards and regulations. My invention, therefore also relates to the compliance of cargo pallet and cargo container to these regulations. Here, cargo pallet and cargo container are terms used herein interchangeably.
a. Description of the Related Art
Governmental regulations and rules require cargo to be loaded and constrained in aircraft using regulated standard pallet and container bases in order to facilitate safety, cargo movement, handling, storage, and convenience. The container bases are sized to fit within designated area or cargo bays inside the aircraft according to size and weight distribution allowances and aircraft design.
Regulations and rules also require that the palletized bases be restrained in their bay from vertical, side and forward movements. Most existing containers used for interstate transportation must meet certification standards for load capacities and positive side vertical restrains. For this purpose, a standard pallet base has holddown areas or strips extending horizontally from the outboard edges and sides at the bottom of the base with strap slots used for restraining purposes. Vertically restraining the upward motion of the pallets at these side edges is important, since the reaction loads of locked pallets must distribute the forces within the adjacent floor beams of the aircraft. Existing pallets and containers without side vertical restraints are restrained for vertical up-gust loads only by the end latches. This configuration transfers vertical up-gust loads on the closest floor beams at the ends of the pallets and containers which under some circumstances, can exceed maximum tolerances leading to failure. Moreover, existing pallets and containers without side vertical restrains are restrained for vertical couple arising from forward-aft loads only by the end latches. Hence, all vertical kick loads in crash conditions are transferred through the end latches to the closest floor beams, leading in most cases to over-loading and failure. It is therefore necessary to have a bulkhead or barrier with sufficient strength to restrain the cargo in a crash condition in the present art.
On each bay, horizontal lipped slots on near the base of the bay provide vertical restrain means. These receive standard outboard edges of the pallet to constrain upward pallet movement within the bay. These lipped slots presume the size and shape of the pallet outboard edges to be straight within the tolerance specified as a receiving gap for the pallet. Both the side lipped slots and pallet outboard edges must be within 0.25 of an inch to ensure positive vertical contact necessary to restrain the pallet and to enable the outboard edges to slide within the lipped slots as the pallet is secured. If the outboard edges of the pallet become distorted or broken from use or wear, the pallet will not slide into the lipped slots easily and the pallet may not be correctly placed within the cargo bay. When this happens, the cargo must be reloaded onto a new pallet, the defective pallet is either discarded or the distortion is corrected. This of course becomes impractical at times. Other solutions to secure a pallet with deformed outboard edges, whether approved or not includes removal of the distorted portions of the outward edges by cutting until the horizonal edges of the pallet fit within the lipped slots. Cutting or correction of the distorted areas weakens the pallet and threatens the security of the cargo within the aircraft.
Accordingly, a need exists for an easy, quick and assured means to constrain cargo and container pallets within cargo bays that allows for and adjusts to distorted outboard edges, while safely restraining vertical movement of the pallet within the bay.
More specifically, a means has been sought to find a cargo pallet hold down system having few moving parts, that will adapt to the various deformations of pallets but will lock the pallet to the aircraft bay. Ideally, the system is as strong as needed to constrain fully loaded pallets or containers yet be able to quickly engage and unengaged pallets within bays to facilitate fast loading and off-loading. The system should be adaptable to existing cargo bays to reduce costs of implementation and ease of use as well as function perfectly with normal pallets as well.
Certain other performance requirements are beneficial to an ideal pallet holddown device: the device should be constructed with few parts of commonly available materials and the operation should be easy to understand and tolerate misuse.
My system is designed to be installed at existing cargo bays with a minimum of modification of existing bays. Two side frames or walls are mounted along the two sides of the cargo bays to replace the lipped slots. The walls are sized and permanently secured to the bay as described below. Normal load carrying rollers to facilitate pallet movement within the cargo areas may be left under the bay. My system uses specially designed cams which are attached to the inside walls of the frames instead of the lipped slots. The cams are circular on the top or upper portion but have an extended or tongue shaped elongated portion on the lower portion of the cam. A shock absorbing, bumper attached to the lower portion of the cam engages the upper surface of the pallet to eliminate metal to metal contact and noise. The cams are attached to the inside of the walls above the entrance way of the pallet. In the unlocked position each cam with bumper is free to rotate. As a pallet is moved into the bay, the bumpers are urged by the pallet to ride on the outboard edges of the pallet, rotating the cams according to the dimensions and distortions of the edges. After the pallet is safely located within the bay, a locking lever on each side of the bay is rotated to lock the cams with bumpers to the outboard edges of the pallet. This is done by using linear gears or teeth fixed to the underside or bottom of each locking lever which when closed engage similarly contoured gears or teeth configured along the top circular portion of cams. When the locking lever is closed, the teeth engage preventing the cams from rotation and the tongues or elongated portions of the cams with bumpers are thus locked to the upper surface of the outboard edges of the pallet preventing vertical movements of the pallet. With this invention, the distortions and uneven thickness of the outboard edges of the pallet are accommodated by the degree of rotation of the cams. The bumpers absorb any shocks and mechanical impacts of metal to metal. A microswitch in conjunction with the locking means provides a status indicating means for the crew, should there be a question as to whether the holddown device is in the locked or unlocked position.
Accordingly, it is a general object of the present invention to provide an improved cargo pallet retaining means.
More specifically, it is an object of the present invention to provide a palletized cargo or container vertical restraining means that conforms to a pallet even when the outboard edges of the pallet are distorted.
It is also an object to provide an improved hold down device for an aircargo pallet that is simple to operate and easy to use.
It is a further object of my invention to provide an improved hold down device that includes a means to determine whether the hold down device is in a locked or unlocked position.
It is another object of the present invention to attain the foregoing objects and also to provide an improved pallet hold down device that is strong, easy to understand and adaptable in environments where loading and off loading must be done within short time periods.
Because containers and pallets used in interstate commerce are government certified for maximum load capacities with mandatory positive side vertical restrains, my invention ensures that these vertical restrains are met.
My invention also ensures that load capacities and positive side vertical restraints certifications are met as well.
My invention also provides for better distribution of up-gust loads to other floor beams within a cargo bay to relieve excessive loading of the end beams and increased pallet and container loads within the aircraft.
My invention additionally, ensures distribution of kick loads to other floor beams within the bay to reduce loading of the end latches and floor beams, reducing the need in most cases of a crash bulkhead or barrier fore of the cargo.
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description thereof.